I. Field of the Invention
This invention relates to a process for producing O,O'-diacyltartaric anhydride, and to a process for producing O,O'-diacyltartaric acid therefrom.
II. Description of the Related Art
Optically active O,O'-diacyltartaric anhydrides are useful compounds and have various uses. For example, optically active monoamides which are useful as packings of chromatography are obtained by reacting the optically active O,O'-diacyltartaric anhydrides with amines (U.S. Pat. Nos. 4,318,819 and 4,318,820). By reacting an optically active O,O'-diacyltartaric anhydride with a racemic amine, racemic amino acid, racemic hydroxy acid, racemic aminoalcohol and a racemic alcohol, respectively, diastereomers are formed, and these diastereomers can be optically resolved by chromatography or by fractional crystallization. For example, it has been reported that .beta.-blocker which is an aminoalcohol can be optically resolved by chromatography (J. Chromatogr. 316, P605-616 (1984)), and that thymolol which is also a .beta.-blocker is optically resolved by fractional crystallization (Dutch Patent No. 8500939).
O,O'-diacetyltartaric anhydride and O,O'-dibenzoyltartaric anhydride are known as O,O'-diacyltartaric anhydrides. As the process for producing these O,O'-diacyltartaric anhydrides, (1) a process wherein 1 mole of L-tartaric acid is reacted with 4.9 moles of acetic anhydride in the presence of a concentrated sulfuric acid to produce O,O'-diacetyl-L-tartaric anhydride (Organic Syntheses Coll. Vol. IV p.242 (1963)); (2) a process wherein 1 mole of L-tartaric acid is reacted with 3.2 moles of benzoyl chloride to produce O,O'-dibenzoyl-L-tartaric anhydride (J. Am. Chem. Soc. 55, p.2605 (1933)); and (3) a process wherein 1 mole of tartaric acid is reacted with 2 moles of benzoyl chloride in a solvent and then thionyl chloride is added, the reaction being carried out in the presence of ferric chloride, zinc chloride or aluminum chloride as a catalyst (Hungarian patent No. 34720).
In the processes (1) and (2) described above, not less than 3 moles of an acid anhydride or acid chloride is used per one mole of tartaric acid. Thus, it is necessary to remove the carboxylic acid produced as a by-product, so that it is difficult to obtain optically active O,O'-diacyltartaric anhydride with a high purity. In the process (3), expensive acid halide is necessary. Further, if ferric chloride is used as a catalyst, although the yield is high, the reaction product is undesirably colored. On the other hand, if zinc chloride or aluminum chloride is used as the catalyst, the yield is lower than in the case of using ferric chloride.
On the other hand, optically active O,O' -diacyltartaric acids produced from O,O'-diacyltartaric anhydrides are useful for racemic resolution of amines. Conventionally, O,O'-dibenzoyltartaric acid which is a representative of O,O'-diacyltartaric acids is produced by the following methods: (i) a method in which O,O'-dibenzoyltartaric anhydride is heated in water to hydrolyze the anhydride and the resultant is cooled to obtain crystals of O,O'-dibenzoyltartaric acid (J. Am. Chem. Soc., 55, 2605 (1933)); and (ii) a method in which O,O'-dibenzoyltartaric anhydride is hydrolyzed in a mixed dichloromethane and small amount of water under a pressure of 1.5-5 atm, and then the resultant is cooled to obtain crystals of O,O'-dibenzoyltartaric acid (Hungarian patent 22147).
In the above-described method (i), upon hydrolysis of O,O'-dibenzoyltartaric anhydride, the produced O,O'-dibenzoyltartaric acid is separated as an oil. When this oil is crystallized, agglomerates of crystals are formed, and the crystals are adhered to the walls and to the stirrer of the apparatus so that they cannot be removed from the reaction apparatus. Thus, the operability is low, so that this process is not suited for industrial production. On the other hand, in the above-described method (ii), although the operability is good, harmful dichloromethane is used in a large amount and the yield per one batch is low.